Writing instrument



FIG. 1 is a front view of a writing instrument according to this design;

FIG. 2 is a right side elevational view, the left side being a mirror image thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a plan view thereof;

FIG. 5 is a bottom view thereof;

FIG. 6 is a right side elevational view with the writing tip extended; and,

FIG. 7 is a perspective view of FIG. 1. 

The ornamental design for a writing instrument, as shown and described. 